Currently considered
unbreakable, a code encryption technique called "steganography" is used
to bury a message in a digital image, audio, or video file. The sender
uses a unique key to encode the file and then posts it somewhere on
the Internet (e-Bay, discussion group, etc.). The receiver visits the
site, downloads the file and uses a matching key to decode the message.
The boys at NSA aren't too happy about this one.